What's a penny nail?

Q. Not an urgent question, but why are nails sometimes called by the “penny” such as a 16 penny nail. Everyone seems to have a slightly different answer, so I am asking you.

A. Back in the 15th Century in England, nails were sold by the amount of money it cost to purchase “long 100” nails. At that time, the small monetary unit was the penny, abbreviated by the letter “d” which had come from the Roman coinage word denarius. Note that 240 pennies equaled 1 pound sterling. Also, due to a Germanic influence and some effort to work with base 12 instead of base 10, the quantity of “long 100” actually meant 120. (A lot of recent info about pennyweight for nails misses this point.)

So, a 16 penny (16 d.) nail is one that cost 16 pennies for 120 nails.

Today we have converted pennies into the length, so all 16 d. nails are 3-1/2 inches long. The length increases ¼ inch for each increase of 1 d up to 10 d. Then each increase in 2 d. is ¼ inch. At 20 d. each 10 d. increases the length by ½ inch. There is no specification about diameter.

2 d. = 1” long

4 d. = 1-1/2”

10 d. = 3”

12 d. = 3-1/4

16 d. = 3-1/2”

20 d. = 4”

Wow! Confusing indeed without a good memory. So, today, most nails are sold by length and diameter and no reference is made to penny. There is no specification about diameter.